How to avoid nginx "upstream sent too big header" errors?

Question

I'm running nginx, Phusion Passenger and Rails.

I am running up against the following error:

upstream sent too big header while reading response header from upstream, client: 87.194.2.18, server: xyz.com, request: "POST /user_session HTTP/1.1", upstream: "passenger://unix:/tmp/passenger.3322/master/helper_server.sock

It is occuring on the callback from an authentication call to Facebook Connect.

After googling, and trying to change nginx settings including proxy_buffer_size and large_client_header_buffers is having no effect.

How can I debug this?

Solution 1

Came across this error recently.

Since Passenger 3.0.8 there is now a setting that allows you to set the buffers and buffer size. So now you can do

http {
    ...
    passenger_buffers 8 16k;
    passenger_buffer_size 32k;
}

That resolved the issue for me.

Solution 2

Try to add this to the config:

http {
    ...
    proxy_buffers 8 16k;
    proxy_buffer_size 32k;
    }

Solution 3

Maybee adding this will make it work, how are you connecting to upstream? http, fastcgi or something else?

http {
    ...
    fastcgi_buffers 8 16k;
    fastcgi_buffer_size 32k;
}

Solution 4

fastcgi_buffers 16 16k;
fastcgi_buffer_size 32k;

Solution 5

This is everything I have come to understand about this error in the last 2 years:

upstream sent too big header while reading response header from upstream is nginx's generic way of saying "I don't like what I'm seeing"

1. Your upstream server thread crashed
2. The upstream server sent an invalid header back
3. The Notice/Warnings sent back from STDERR broke their buffer and both it and STDOUT were closed

3: Look at the error logs above the message, is it streaming with logged lines preceding the message? PHP message: PHP Notice: Undefined index: Example snippet from a loop my log file:

2015/11/23 10:30:02 [error] 32451#0: *580927 FastCGI sent in stderr: "PHP message: PHP Notice:  Undefined index: Firstname in /srv/www/classes/data_convert.php on line 1090
PHP message: PHP Notice:  Undefined index: Lastname in /srv/www/classes/data_convert.php on line 1090
... // 20 lines of same
PHP message: PHP Notice:  Undefined index: Firstname in /srv/www/classes/data_convert.php on line 1090
PHP message: PHP Notice:  Undefined index: Lastname in /srv/www/classes/data_convert.php on line 1090
PHP message: PHP Notice:
2015/11/23 10:30:02 [error] 32451#0: *580927 FastCGI sent in stderr: "ta_convert.php on line 1090
PHP message: PHP Notice:  Undefined index: Firstname

you can see in the 3rd line (from the 20 previous errors) the buffer limit was hit, broke, and the next thread wrote in over it. Nginx then closed the connection and returned 502 to the client.

2: log all the headers sent per request, review them and make sure they conform to standards (nginx does not permit anything older than 24 hours to delete/expire a cookie, sending invalid content length because error messages were buffered before the content counted...)

examples include:

<?php
//expire cookie
setcookie ( 'bookmark', '', strtotime('2012-01-01 00:00:00') );
// nginx will refuse this header response, too far past to accept
....
?>

and this:

<?php
header('Content-type: image/jpg');
?>

<?php   //a space was injected into the output above this line
header('Content-length: ' . filesize('image.jpg') );
echo file_get_contents('image.jpg');
// error! the response is now 1-byte longer than header!!
?>

1: verify, or make a script log, to ensure your thread is reaching the correct end point and not exiting before completion.

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